How to maintain long-term relationships with the suppliers?

1) Always place your order so there is plenty of time for it to be processed. 3 days before the order deadline is the latest I would aim for.

2) Double check all orders berfore submitting the order to the supplier. Check type, quantity, unit price, overall price (including delivery). Avoid changinging orders once they are submitted, if you do need to however do it ASAP.

3) Always pay bills before the due date, 3 days before due is all that's needed. If you are going to be late or are submitting a bank transfer (that may take a few days to clear) let the supplier know.

4) If you have problems with any product the supplier is delivering (including delivery issues, damage, cost increases, quality etc) talk to them about it. Dont be rude, offensive or angry about it. Start by confirming your loyalty to that supplier/ complimenting the service he provides (if warranted), address the problem, request a solution, listen and than thank them at the conclusion of the conversation e.g

"Hi Tom, its Name here from Company X, how are you? I've been doing business with you for a long time now and I hope that continues, your always on time and the products are first class but I have an issue with the last order. All the boxes seem to be pretty banged up in the edges and not only does it look second hand but the customers nearly always want a discount. Is there anyway we can take a bit of extra care with them? Maybe I could give your delivery driver a hand unloading the truk or something"

Remember it might take time to work out the details, be patient.

5) Communication should be clear and honest. I like to place my orders via phone which allows me to actual converse with my supplier, confirm via email which makes everything clear. Check that this doesnt annoy your supplier as some might see it as unnecessary double digging.